1. Field of the Invention
The present invention relates to a drain valve, and particularly to a drain valve which is mounted on a toilet water tank to control water and which is water-saving and is adapted for all types of water tanks.
2. Related Art
Nowadays toilet water tanks are popularly used to reserve water for flushing toilet bowls. Drain valves are provided in the water tanks. By operating activating elements, the drain valves are driven to control water flowing out of water tanks for flushing the toilet bowls.
As shown in FIG. 8, a conventional drain valve 40 comprises a cover 41. A lift portion 411 is formed on the top of the cover 41. A chain 42 has an end coupled with the lift portion 411 and another end coupled with a link pole 52 of a handle 51 above a water tank 50. A pair of support arms 412 is formed on an edge of the cover 41 and parallel to each other. Each support arm 412 defines a notch 413 at a bottom thereof for clamping a rotating element 531 of an overflow tube 53 in the water tank 50.
A float 43 is provided below the cover 41, and a stop pad 44 is formed between the float 43 and the cover 41. A flow hole 431 is defined at center of a bottom of the float 43 for allowing water in or out. A vent hole 432 is defined at a top of the float 43.
The handle 51 is activated to open the cover 41, and the preserved water in the water tank 50 flows out from the drain hole 54. At the same time, the preserved water also flows through the flow hole 431 and into the float 43. Subsequently, interior air in the float 43 is pulled out from the vent hole 432 by water. When weight of water in the float 43 reaches a predetermined value, the cover 41 pivots and stops the drain hole 54, and the water tank begins to preserve water therein.
The drain valve 40 can control water flowing or stopping. However, width of the vent hole 432 can not be adjusted, and the air in the float 43 is pulled out at fixed velocity. It is uncontrollable when the cover 41 pivots to stop the drain hole 54. So it is as well uncontrollable how much water in the water tank 50 is drained. Such a conventional drain valve does not save water and is uneconomical.